Diogenes, the author of the following work, was a native (as is generally believed) of Laërte, in Cilicia, from which circumstance he derived the cognomen of Laërtius. Little is known of him personally, nor is even the age in which he lived very clearly ascertained. But as Plutarch, Sextus Empiricus, and Saturninus are among the writers whom he quotes, he is generally believed to have lived near the end of the second century of our era: although some place him in the time of Alexander Severus, and others as late as Constantine. His work consists of ten books, variously called: The Lives of Philosophers, A History of Philosophy, and The Lives of Sophists. From internal evidence (iii. 47, 29), we learn that he wrote it for a noble lady (according to some, Arria; according to others, Julia, the Empress of Severus), who occupied herself with the study of philosophy, and especially of Plato.
Diogenes Laërtius divides the philosophy of the Greeks into the Ionic, beginning with Anaximander, and ending with Theophrastus (in which class, he includes the Socratic philosophy and all its various ramifications); and the Italian, beginning with Pythagoras, and ending with Epicurus, in which he includes the Eleatics, as also Heraclitus and the Sceptics. From the minute consideration which he devotes to Epicurus and his system, it has been supposed that he himself belonged to that school.
